Metal gasket and production method therefor
Provided is a metal gasket including, expressed in mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less (including 0%), S: 0.01% or less (including 0%), Ni: 25.0-60.0%, Cr: 10.0-20.0%, either Mo or W alone, or both Mo+W/2: 0.05-5.0%, Al: more than 0.8% to 3.0% or less, Ti: 1.5-4.0%, Nb: 0.05-2.5%, V: 1.0% or less (including 0%), B: 0.001-0.015%, Mg: 0.0005-0.01%, S/Mg: 1.0 or less, N: 0.01% or less (including 0%), and O: 0.005% or less (including 0%), with the remainder being Fe and unavoidable impurities. The metal gasket has a metal structure in which a precipitate γ′ phase having an average equivalent circle diameter of 25 nm or larger is not present within the austenite base.
1. A metal gasket consisting of, in terms of % by mass, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less, S: 0.01% or less, Ni: 25.0% to 60.0%, Cr: 10.0% to 20.0%, one or both of Mo and W satisfying Mo+W/2: 0.05% to 5.0%, Al: 1.6% to 3.0%, Ti: 1.5% to 3.0%, Nb: 0.3% to 2.5%, V: 1.0% or less, B: 0.001% to 0.015%, Mg: 0.0005% to 0.01%, wherein S/Mg: 1.0 or less, N: 0.01% or less, O: 0.005% or less, and a remainder consisting of Fe and unavoidable impurities,
wherein the metal gasket has a metal structure having an austenite matrix,
wherein either:
a precipitate γ′ phase is not present in the austenite matrix; or,
if a precipitate γ′ phase is present in the austenite matrix, the precipitate γ′ phase present in the austenite matrix has an average equivalent circle diameter smaller than 25 nm,
wherein the precipitate γ′ phase consists of constituent elements selected from the group consisting of Ni, Al, Ti, and Nb, and
wherein the metal gasket has a thickness of 1 mm or less.
2. The metal gasket according to claim 1 , wherein an average equivalent circle diameter of the precipitate γ′ phase is smaller than 20 nm.
3. A method for producing the metal gasket of claim 1 consisting of, in terms of % by mass, C: 0.10% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less, S: 0.01% or less, Ni: 25.0% to 60.0%, Cr: 10.0% to 20.0%, one or both of Mo and W satisfying Mo+W/2: 0.05% to 5.0%, Al: 1.6% to 3.0%, Ti: 1.5% to 3.0%, Nb: 0.3% to 2.5%, V: 1.0% or less, B: 0.001% to 0.015%, Mg: 0.0005% to 0.01%, wherein S/Mg: 1.0 or less, N: 0.01% or less, O: 0.005% or less, and a remainder consisting of Fe and unavoidable impurities,
wherein the method comprises:
plastic working of a material for cold rolling having the composition into a thin plate shape by performing cold rolling on the material; and performing a process of forming the material into a metal gasket shape having a thickness of 1 mm or less.
4. The method for producing a metal gasket according to claim 3 , wherein the precipitate γ′ phase has an average equivalent circle diameter of smaller than 20 nm.
5. The method for producing a metal gasket according to claim 3 , further comprising performing a solution treatment on the metal gasket subjected to the process of forming into the metal gasket shape at 900° C. to 1150° C.
6. The method for producing a metal gasket according to claim 3 , further comprising performing an aging treatment on the metal gasket subjected to the process of forming into the metal gasket shape at 700° C. to 850° C. for 0.5 to 5 hours.
7. The method for producing a metal gasket according to claim 4 , further comprising performing a solution treatment on the metal gasket subjected to the process of forming into the metal gasket shape at 900° C. to 1150° C.
8. The method for producing a metal gasket according to claim 4 , further comprising performing an aging treatment on the metal gasket subjected to the process of forming into the metal gasket shape at 700° C. to 850° C. for 0.5 to 5 hours.